Ken Sejkora

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• Ken Sejkora
• Entergy Nuclear Northeast Pilgrim Station
• Presented at the 16th Annual RETS-REMP Workshop
• Mashantucket, CT / 26-28 June 2006

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Reason for Concern

• Issue of tritium in groundwater has crossed
  jurisdictional boundaries NRC, EPA, state
  radiation control programs are involved
• Various limits exist governing effluent
  compliance, safe drinking water standards, and
  dose/risk assessment
• Recognize the different limits, reasons for
  differences, and implications/applicability

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EPA Drinking Water Standard from the beginning

• Specified in 40 CFR 141.25
• Refer to www.epa.gov/safewater/rads/radfr.pdf
• 20,000 pCi/Liter, assumed to yield committed dose
  of 4 mrem/yr
• Based on drinking water consumption of 2
  liters/day 730 liters/yr
• 20,000 pCi/L 730 L/yr 1.46E7 pCi/yr
• 4 mrem / 1.46E7 pCi 2.74E-7 mrem/pCi

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EPA Drinking Water Standard why its important

• Standard limit adopted by state regulatory
  agencies often takes precedence over ODCM limits
  if groundwater is involved
• Used as basis for tables in standard ODCM
  guidance NUREG-1301/1302
• Table 3.12-2, Reporting Levels 20,000 pCi/L
  for drinking water 30,000 pCi/L for non-DW
• Table 4.12-1, Lower Limit of Detection set at
  1/10 of Reporting Level 2,000 pCi/L for DW
  3,000 pCi/L for non-DW.

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EPA Drinking Water Standard where did it
come from?

• Roots in ICRP-2, circa late 1950s
• Second generation derivative of NRC maximum
  permissible concentration (MPC) value
• 1 MPC 500 mrem/yr total body
• Early MPC for tritium 3E-3 uCi/mL
• (4 mrem / 500 mrem) 3E-3 uCi/mL 2.4E-5
  uCi/mL 24,000 pCi/L
• Rounded to 20,000 pCi/L one significant figure
• Gray-hair phenomenon derivation not
  documented, exists only in recollection of
  experts involved

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Other ICRP-2 based Factors

• Direct activity-to-dose factors
• not back-calculated from concentration limit
• Age-specific dose factors
• Regulatory Guide 1.109, Ingestion dose factors,
  Tables E-11 through E-14
• Adult 1.05E-7 mrem/pCi Child 2.03E-7 mrem/pCi
  
• Teen 1.06E-7 mrem/pCi Infant 3.08E-7 mrem/pCi

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Other ICRP-2 based Factors continued

• LADTAP Factors refinement of RG-1.109 factors
• Adult 5.99E-8 mrem/pCi Child 1.16E-7 mrem/pCi
• Teen 6.04E-8 mrem/pCi Infant 1.76E-7 mrem/pCi
• RG-1.109 and LADTAP dose conversion factors are
  the de facto values used in most plants ODCMs,
  effluent control programs, and effluent dose
  calculation software

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ICRP-30 based Factors

• Based on ICRP-26 standard man approach,
  occupational exposure circa early 1970s
• Single age class adult male
• Basis for current values in 10CFR20 Appendix B,
  and EPA Federal Guidance Report 11
• Ingestion DCF 6.40E-8 mrem/pCi
• Table 2, Column 2 Concentration Limit - Public
  1E-3 uCi/mL, or 1,000,000 pCi/L assumed to
  yield committed dose of 50 mrem/yr

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ICRP-60/72 Factors

• Based on ICRP-60 metabolic models most modern,
  circa late 1990s
• Non-occupational exposure, latest risk quality
  factors, multiple age classes,
• Adult 7.09E-8 mrem/pCi 5-yr 1.25E-7
  mrem/pCi
• 15-yr 7.07E-8 mrem/pCi 1-yr 2.04E-7
  mrem/pCi
• 10-yr 9.06E-8 mrem/pCi Infant  2.79E-7
  mrem/pCi
• Standard among international community, but not
  widely adopted in USA, nor endorsed by NRC
  however, adopted in EPA FGR-13

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Side-by-side Comparison

• EPA DW Standard 2.74E-7 mrem/pCi
• Reg Guide 1.109
• Adult 1.05E-7 mrem/pCi Child 2.03E-7 mrem/pCi
• Teen 1.06E-7 mrem/pCi Infant 3.08E-7 mrem/pCi
• LADTAP
• Adult 5.99E-8 mrem/pCi Child 1.16E-7
  mrem/pCi
• Teen 6.04E-8 mrem/pCi Infant 1.76E-7 mrem/pCi
• ICRP-30 6.40E-8 mrem/pCi
• ICRP-72
• Adult 7.09E-8 mrem/pCi 5-yr 1.25E-7
  mrem/pCi
• 15-yr 7.07E-8 mrem/pCi 1-yr 2.04E-7
  mrem/pCi
• 10-yr 9.06E-8 mrem/pCi Infant 2.79E-7
  mrem/pCi

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Which Limit to Use?

• RG-1.109/LADTAP for ODCM effluent release
  compliance, possible extension to REMP samples
• EPA Safe Drinking Water Standard adopted by most
  state programs comes into play if offsite
  groundwater is involved
• ICRP-72 is not used (except for EPA FGR-13),
  despite being most modern and based on best
  available technology
• When dealing with the recent groundwater issue,
  one could argue we should use the most up-to-date
  methodology and science available.

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Beware

• Organically-bound tritium
• Strontium-90

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Organically-bound tritium

• Existing limits (EPA, NRC) are based on tritium
  in the form of tritiated water
• High metabolism, rapid turnover/clearance from
  body
• Relatively low dose impact
• Organically-bound tritium, once incorporated into
  tissue, has much longer residence time in body
• More time Higher dose impact
• Could result in lower limits than those based on
  conventional tritiated water metabolism
• Organically bound tritium is not of concern in
  drinking water, but could result in modifying
  concentration limits to account for higher
  dose/risk once in the body

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Strontium-90

• Exists at low levels in environment from weapons
  testing in 1950s through 1970s often seen in
  REMP samples
• Has been detected at low levels in groundwater by
  some licensees
• There is a separate EPA drinking water standard
  for Sr-90 listed in 40CFR141
• According to Federal Register, based on
  assumption that 8 pCi/L Sr-90 will yield 4
  mrem/yr to bone marrow.
• Similar rationale to that used for H-3 at 20,000
  pCi/L

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Strontium-90 -- error in drinking water
standard?

• 1 MPC 1500 mrem/yr critical organ (bone)
• MPC for Sr-90 3E-7 uCi/mL
• (4 mrem / 1500 mrem) 3E-7 uCi/mL 8E-10
  uCi/mL 0.8 pCi/L, NOT 8 pCi/L
• 8 pCi/L 730 L/yr 5840 pCi/yr intake
• 5840 pCi/yr 7.58E-3 mrem/pCi 44 mrem/yr, NOT
  4 mrem/yr
• EPA standard for Sr-90 appears to be 10X too
  high!
• Compliance with the EPA standard of 8 pCi/L would
  exceed the 10CFR50 Appendix I organ dose limit of
  15 mrem/yr by about 3X

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Summary

• Several limits exist for tritium in water
• EPA drinking water limit 20,000 pCi/L
• NRC effluent limit 1,000,000 pCi/L (1E-3
  uCi/mL)
• Fractional limits imposed by states?
• Various limits are based on different
  assumptions, different bases
• EPA 20,000 pCi/L 4 mrem/yr, based on ICRP-2
• NRC 1,000,000 pCi/L 50 mrem/yr, based on
  ICRP-30

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Summary (continued)

• Other nuclides, forms may come into play
• Organically-bound tritium, Sr-90
• Concern about non-conservative Sr-90 drinking
  water standard
• If one has to deal with multiple nuclides, it
  makes sense to use a single standard, and
  presumably the most modern one ICRP-72

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Conclusion

• This IS a dose issue